COMPENSATORY GROWTH AND CARCASS QUALITY IN GROWTH-RESTRICTED AND REFED BEEF STEERS

Beef steers were fed in two phases 1) to determine the relative import ance of changes in DMI, gastrointestinal tract fill, energy expenditur es, and composition of gain in the compensatory growth phenomenon, 2) to compare the effects of growth restriction due to ad Libitum consump tion of a low-energy (low-concentrate) diet to those of limited intake of a high-energy (high-concentrate) feed, and 3) to examine changes i n carcass composition and quality resulting from different types of gr owth restriction. During the growing phase (237 to 327 kg), steers wer e fed either a high- (C) or low- (F) concentrate diet. Diet F was avai lable for ad Libitum consumption (FA) and diet C was available either for ad libitum consumption (CA) or on a Limited basis (CL) to match th e live weight gains by the FA group. During the finishing phase (327 t o 481 kg), all steers received diet C, either for ad Libitum consumpti on (CA) or restricted (CL) to 70% of the intake by the corresponding C A steers. Backfat thickness was markedly reduced (P <.001) by final fe ed restriction (7.4 and 6.9 mm for CL-CL and FA-CL respectively), comp ared with CA-CA (12.6 mm). Backfat also was lower in CL-CA (11.6 mm, P <.10) and FA-CA (9.9 mm, P <.05) than in CA-CA steers. Conversely, ma rbling scores were similar among groups, except for the FA-CL steers, which had lower marbling scores than FA-CA and CL-CA steers (P <.05). Higher DMI following growth restriction were accompanied by increased rates of live weight (+54 and +27%) and empty body weight (EBW; +57 an d +43%) gain for CL-CA and FA-CA steers, respectively, compared with C A-CA steers. Gain:feed (EBW basis) were improved in some restricted/re fed groups (+30, +13, and +10%, for CL-CA, CL-CL, and FA-CA, respectiv ely) relative to CA-CA. Increased DMI played a major role in the compe nsatory gain response in both CL-CA and FA-CA groups. Maintenance requ irement was reduced (-17%) in CL-CA and increased in the FA-CA group ( +21%); both changes affected the magnitude of compensatory gain in tho se animals. In contrast, composition of gain had little or no effect o n the compensatory gain response. Programmed feeding can be used to ma nipulate carcass quality, but low-concentrate feeding during the growi ng phase may impair overall feedlot performance.